(c) Acute lymphoblastic leukemia (ALL). (i) Given the poor prognosis of adults (≥21 years) with ALL, adults in 1st or greater complete remission will be eligible.. CR is defined as an M1 marrow (<5% blasts), no evidence of extramedullary disease, and an absolute neutrophil count ≥ 1.0 x 109/L. Complete remissions without platelet recovery (CRp) will be considered remissions (ii) Given the generally good prognosis of children (<21 years) with ALL, they will have to meet one of the criteria listed below. Additionally, children who are enrolled on a COG ALL trial for newly diagnosed or relapsed disease will have to meet the criteria for BMT outlined in that trial. CR is defined as an M1 marrow (<5% blasts), no evidence of extramedullary disease, and an absolute neutrophil count ≥ 1.0 x 109/L. Complete remissions without platelet recovery (CRp) will be considered remissions.